We have a 13 year old granddaughter who has been to church with us several times. She has heard of Jesus but yet the concept of sin is not in her realm of understanding. She is very much in the here and now and her concept of time is vague at best. Accountability is also a very vague concept at best.
As she grows older it will be doubtful that she will get beyond where she is now mentally. If I understand accountability and the need for confession and embracing Jesus as savior she will never be able to take that step. I would expect to be with her when we are all called home. Would that be a valid supposition?
Being a just God, our Lord does not hold people accountable for something they don’t have the ability to understand. If your grand daughter lacks the mental capacity to comprehend the nature of sin and salvation, then in the Lord’s eyes she’s like a little child and belongs to Him. You should expect that she’ll go with you in the Rapture.